Combined amplification and tuning controls



COMBINED AMPLIFICATION AND TUNING CONTROLS Filed Oct. 17, 1934 7QJ//V/IZ M INVENTOR ATTORNEY Patented July 19, 1938 UNITED STATES 12,124,211 COMBINED AMPLIFICATION AND TUNING CONTROLS Walter van B.Roberts, Princeton, N. J., as'signor to Radio Corporation of America,a'corporation v of Delaware Application October 17, 1934, SerialNo.748,610

- 1 claim; (01. 179 -171) My present invention relates to uni-controlledconnection with the drawing in which I have in-,

tuning and amplification control adjustments for radio receivers, andmore particularly to novel and improved devices for'correlatingpthetuning and radio frequency energy transfer characteristics of theselector networks of radio receivers.

One of the main objects of my present invention is to provide capacitycoupled radio frequency amplifiers wherein the'capacity coupling existsbetweena following tunable radio, frequency selector network and a'preceding non-tunable plate circuit of a radio frequency amplifier; theenergy transfer characteristic and the tuning characteristic of thecoupled circuits being varied in such a manner, and by such devices,that a predetermined transfer characteristic over the entire tuningrangeis secured with the capacity coupling as small as possible at' thehigh frequency end of the tuning range, and as" large as convenient atthe low frequency end.

Another important object of the invention is to provide an adjustablecapacity device between ,v selector circuit of a radio frequencyamplifier, the

tunable circuit being arranged for coupling to the untuned plate circuitof a preceding amplifier, the tuning condenser being providedwith.

The novel features which I believe to be char acteristic of my inventionare set forth in particularity in the appended claim, the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin dicated diagrammatically several circuit organizations whereby myinvention may be cariedinto effect.

In the drawing:-

Fig. 2 shows the circuit diagram of the amplifier embodying onemechanical form of a come, 1

bined tuning and amplification control'device.

Referring now to the accompanying drawing, wherein like referencecharacters in the dif' ferent figures designate similar circuitelements,

the radio frequency amplifier of Fig. 1 shows a pair ofscreen grid tubesI and 6 capacitatively coupled by a condenser C. The input electrodes,of amplifier tube 1 may be considered arranged for coupling to anysource of signal energy. For example, the amplifier network of Fig.l'may be considered as the radio frequency amplifier of asuperheterodyne receiver. In such case the .output electrodes of tube 6may be adapted for connection to the first detector of the set, or thetube 6 may itself be the first detector Of course, the signal collector.may, in that case, be connected to the input electrodes of amplifier l,and a tunable selector circuit may be connected to the input ofamplifier I. a l

If the amplifier network is in areceiyer of the tuned radio frequencytype, then the amplifier I- may be the first tunable radio frequencyamplifier, and the tube 6 may be the'secondtunable radio frequencyamplifier, or it may be the dey tector. be understood as havinga wideapplicability; whatever the nature of the circuits which are coupled,the problem to be solved by the present invention is tovary the tuningand radio fre-' quency energy transfer characteristics of the couplingnetwork so as to obtain a desired energy transfer characteristic overthe tuning range of the receiver.

The plate of amplifier l is connected to the low potential side of theusual grid biasing network 2' through a path which includes the radiofrequency choke 3 and the source of plate voltage 4. The frequencyselection network comprises the coil 5,and the variable tuning condensert connect:

, ed in shunt with the coil 5; the tunable circuit be ing connected inseries between the input grid ofv tube 6 and the low potential'side ofthe grid biasing network I. The coupling condenser C connects the plateside of choke 3 to the high alternating voltage side of the followingtunable cir-- cuit. The problem presented for solution by the In anycase the present invention istoinvention of the present application isto vary the tuning of the tunable input circuit of tube 6 over thetuning range of the receiver, and yet maintain a desired andpredetermined radio frequency energy transfer through the couplingcondenser C over the entire tuning range of variable condenser t.

Fig. 1 shows the manner of securing such a relationship, or rather sucha correlation of tuning and energy transfer, and it is also accomplishedin a simple, effective and economical manner. An auxiliary condenser Sis connected across the plate circuit of tube I, and in shunt withcondensers C and t. The magnitudes of condensers S and C are so chosen,and their rates of variation are uni-controlled with the variation ofcondenser t in such a manner, that a predetermined energy transfercharacteristic can be secured. Such a characteristic may be of theuniform, or flat, gain type; that is to say, the amplification of thesignal energy will be substantially uniform over the tuning range of thereceiver embodying the amplifier network shown in Fig. 1.

To preserve as large a tuning range as possible, say over the broadcastband which is between 500 and 1500 kilocycles, the value of condenser Cshould be as small as possible at the high frequency end of the tuningrange of the receiver; it should be as large as convenient at the lowfrequency end. It is not believed necessary for the purposes of thepresent application to present the theoretical considerations whichsupport the premise that for a given set of other conditions, the valueof condenser C required for a given amplification depends upon the valueof condenser S; It will be sufficient to point out that such a premiseis established in an analysis entitled Maximum Amplification InCapacity-Coupled Circuits, appearing on page 20 of Electronics for July,1931.

It can now be stated that it is the purpose of the present invention tovary the capacity value of condenser S in such a fashion that for adesired amplification characteristic the condenser C will be required toassume a small value at the high frequency end of the tuning range and arelatively large value at the lower frequency end. In Fig. 1 the dottedlines U designate the mechanical uni-control arrangement for varying thethree condensers. This mechanical variation of the condensers should, ofcourse, be accomplished in an economical, effective and simple manner,and

without the use of sliding contacts or pigtail connections.

In Fig. 2 such a mechanical construction is shown. The normal condenserconstruction is this purpose, and the shaft 9 will be understood asadditionally being connected to, and supporting on it, the rotors of thetuning condensers of other amplifier stages. and I3 may be used inconjunction with each tuning condenser of each stage. For the purposeofsimplicity, however, the construction between a given pair ofamplifier tubes is only considered. It will also be understood that itis un- The auxiliary plates l4" necessary to show the side view of thecondenser plates, or the housing construction of the plates becausethose skilled in the art are fully aware of the manner of constructingsuch condensers of the variable type.

The profile of the plates of condenser S are cut to give any desiredvariation of condenser S with respect to the variation of tuningcondenser t. The two condenser assemblies S and t are located far enoughapart on the shaft so that the stray capacity between stators is smallerthan the smallestvalue of coupling capacity desired at C. Thedisposition of a grounded shield 8 between the adjacent stators l3 andI2 will reduce the required separation, but the separation should not bereduced too much, or the minimum capacity of condensers S and t will beincreased too much by the close proximity of their stators to thegrounded shield 8.

The variable capacity C consists of the metal conductor composed of twoplates l6, l6 metallically connected together by a bolt l5. Thisconductor is insulated from shaft 9, although mechanically adjustabletherewith. A block of insulation material l0, such as a collar ofinsulation material, is carried by the shaft 9, and the bolt I5 isdisposed within the collar.

The collar I0 is rigidly connected to shaft 9 so that adjustment ofshaft 9 results in movement of plates 16, lfi' with rotors l4 and H.Plate I6 is disposed adjacent the end stator'l2 of condenser 15, whileplate i6 is disposed adjacent the end stator I3 of condenser S. Theplates l6 and Hi cooperate with their adjacent stator plates to providethe condenser C. Hence it will be seen that as'shaft 9 is varied thecapacity values of condensers S, C and t are varied. The conductorcomprising plates l6 and I6 is not electrically connected to any portionof the circuit, but serves to vary the effective separation between thestadenser S to the high alternating potential side of the tunablecircuit of amplifier 6. The value of this inter-stator capacity isvaried by the plates It and I6, and the disposition of these platesbetween the adjacent end stators is varied at a rate dependent upon therate of variation of the capacities of condensers S and t. It is notbelieved necessary to go into any further detail concerning specificprofiles for the blades of the condensers, since such profiles can beeasily determined by those skilled in the art when it has been decidedwhat the amplification characteristic is to be; As stated before aspecific type of such characteristic is one that is uniform over thereceiver tuning range, and in Fig. 2 it is to be understood that thecapacity values of condensers S and C are varied with the variation ofcondenser t so that the transfer of radio frequency energy to the outputcircuit of tube 6 is substantially uniform over the tuning range of thereceiver. It will now be appreciated that this relation of amplificationand tuning has been secured in a highly economical and simplefashion,and without sliding contacts.

For a further disclosure of the manner of constructing a variablecondenser of the type shown in Fig. 2, reference is made to applicationSerial No. 387,148 of J. L. Bonanno, filed August 20, 1929,

issued as Patent No. 2,040,426 o'nMay 12, 1936, wherein there isclaimed, as well as disclosed, the

type of variable condenser shown in Fig. 2, and

network; in the present application the variable condenser constructionof the Bonanno patent is used to secure a predetermined amplificationcharacteristic over the tuning range of the receiver. r 7

While I have indicated and described several systems for carryingmyinvention into efiect, it will be apparent to one skilled in the artthat my invention is by nomeans limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention, as set forth in the appendedclaim.

What I claim is: V

In combination in a high frequency network which comprises a first tubehaving an untuned plate circuit which includes a radio frequency chokeand a shunt capacity, a second tube provided with a tunable circuit, acondenser coupling the plate circuit of the first tube to the tunablecircuit, and means including a common control for simultaneously varyingthe value of said shunt capacity, coupling condenser and the tun-

